Condensation apparatus

Abstract

The invention provides an apparatus for increasing the size of gas-entrained particles in order to render the gas-entrained particles detectable by a particle detector, the apparatus comprising an evaporation chamber ( 2 ) and a condenser ( 7 ); the apparatus is configured so that vapour-laden gas from the evaporation chamber can flow into the condenser and condensation of the vaporisable substance onto gas-entrained particles in the condenser takes place to increase the size of the particles so that they are capable of being detected by a particle detector.

The invention claimed is: 
     
       1. Apparatus for increasing the size of gas-entrained particles in order to render the gas-entrained particles detectable by a particle detector, the apparatus comprising:
 an evaporation chamber; 
 a condenser in fluid communication with the evaporation chamber and having an outlet for connection to a particle detector; 
 a heating element and a porous support each of which is disposed within the evaporation chamber, the porous support carrying thereon a vaporisable substance and the heating element being heatable to vaporise the vaporisable substance to form vapour within the evaporation chamber; wherein the porous support surrounds the heating element; 
 a first inlet for admitting a stream of carrier gas into the evaporation chamber to carry vapour through to the condenser; 
 a second inlet which is downstream of the porous support and through which a stream of sample gas containing gas-entrained particles can be introduced; 
 the apparatus being configured so that condensation of the vaporisable substance onto the gas-entrained particles in the sample gas takes place in the condenser to increase the size of the particles so that they are capable of being detected by a particle detector. 
 
     
     
       2. Apparatus according to  claim 1  wherein a temperature sensor is disposed within the evaporation chamber. 
     
     
       3. Apparatus according to  claim 1  wherein the apparatus is configured such that:
 the second inlet is arranged so that it opens into an intermediate chamber between the evaporation chamber and the condenser; 
 the intermediate chamber is divided by a dividing wall into upstream and downstream sub-chambers, a central hole in the wall providing communication between the sub-chambers, whereby the second inlet opens into the upstream sub-chamber; 
 a third inlet opens into the downstream sub-chamber, the third inlet being connectable to a supply of filtered gas; 
 a nozzle is provided that extends from an exit opening of the evaporation chamber into the condenser to a position in the upstream sub-chamber that is level with or downstream of the second inlet; 
 the downstream sub-chamber contains a cylindrical baffle that is aligned with the said nozzle and the central hole in the dividing wall, and the third inlet opens into a space surrounding the cylindrical baffle. 
 
     
     
       4. Apparatus according to  claim 1  wherein cooling means are provided to assist cooling of the mixture of gases, vapour and particles in the condenser. 
     
     
       5. Apparatus according to  claim 1  wherein the condenser has a surface area to volume ratio which is greater than the surface area to volume ratio of a cylinder. 
     
     
       6. Apparatus according to  claim 1  wherein the condenser is provided with means for removing condensed substance from the interior walls of the condenser. 
     
     
       7. Apparatus according to  claim 1  containing means for varying the temperature of the porous support and/or the temperature of the condenser or its parts in order to control the lower detectable size limit of particles of interest and, therefore, to obtain nano-particle size distributions. 
     
     
       8. An apparatus as defined in  claim 1 , wherein the condenser comprises:
 a condenser body having a condenser inlet, the outlet, and a hollow interior which has an internal length, an internal width and an internal height; the condenser inlet providing fluid communication with the evaporation chamber; 
 an inlet flow distributor tube connected to the condenser inlet and extending across the internal width of the condenser body; and 
 an outlet flow distributor tube connected to the outlet of the condenser body and extending across the internal width of the condenser body; 
 wherein the internal height of the condenser body is less than a corresponding internal height of each of the inlet and outlet flow distributor tubes; 
 inlet and outlet flow distributor tubes each being provided in the walls thereof with one or more slots or holes communicating with the hollow interior of the condenser body so as to provide a flow path from the inlet flow distributor tube through the hollow interior of the condenser and into the outlet flow distributor tube. 
 
     
     
       9. A apparatus according to  claim 8  wherein the internal cross sectional area of each flow distributor tube is greater than the internal cross sectional area (internal width×internal height) of the condenser body. 
     
     
       10. A condensation particle counter comprising an apparatus as defined in  claim 1 . 
     
     
       11. An assembly comprising an apparatus as defined in  claim 1  connected to a particle detector. 
     
     
       12. An assembly comprising a plurality of apparatuses according to  claim 1  connected sequentially or in parallel. 
     
     
       13. Apparatus according to  claim 1  wherein the heating element comprises a rod portion and the porous support surrounds the said rod portion. 
     
     
       14. Apparatus according to  claim 13  wherein the porous support is formed from a porous fabric and comprises a sleeve that fits over the rod portion of the heating element. 
     
     
       15. Apparatus according to  claim 13  wherein the rod portion of the heating element has a hollow interior within which is disposed a heater wire or heater probe and optionally a thermocouple. 
     
     
       16. Apparatus according to  claim 15  wherein a thermally conductive filler is used to hold the heater wire or heater probe and the thermocouple (when present) in place. 
     
     
       17. Apparatus according to  claim 1  wherein the vaporisable substance is selected from dimethyl phthalate, dioctyl phthalate and dimethylsulphoxide.